This invention is related to a magnetron suitable for a micro wave generator of a micro wave application apparatus.
Generally, a magnetron has a getter material for sustaining and obtaining a high degree of vacuum in the chamber. The getter material is formed from mainly titanium powder, zirconium powder or combination of them which are dissolved into a solvent and sintered. Just after sintering the getter material in the chamber, the surface of the getter material is oxidized, in other words, the surface condition is in a state of having adsorbed gases. Under this condition, when the temperature of the getter material reaches to a certain degree, the oxide or the like on the surface are dispersed in the chamber and a new gettering surface is reproduced. (This process is called “activation”). This new gettering surface adsorbs gas molecules. Such gettering effect can be obtained at low temperature (at room temperature). But, in the low temperature condition, as the speed of adsorbents diffusion into the chamber is slower than the speed of adsorbing, the gettering surface is saturated and the gettering effect become not to work. On the other hand, when the getter material gets too high temperature, the getter material melts and evaporates.
As mentioned above, there is a suitable temperature range for effective work of the getter material. The position at which the getter material is mounted is determined in view of the temperature range. For example, in the magnetron disclosed in JP-U-S61-018610 as shown in FIG. 9, a getter material 103 is mounted on an inclined surface of a pole piece 102 mounted on an opening edge of an input side of an anode cylinder 101. The inclined surface is facing to the inner wall of the anode cylinder 101 and electricity is supplied for the cathode part 106 through the input side of the anode cylinder 101. In this reference, such a method is employed in which the getter material 103 is applied to the inclined surface of the pole piece 102 and then sintered, and alternatively in which a getter substrate coated by the getter material 103 is welded on the inclined surface of the pole piece 102. In FIG. 9, a pole piece 104 mounted on the opening edge of the output side of the anode cylinder 101, an anode vane 105 radially disposed inside the anode cylinder 101, a stem ceramic 107 supporting two cathode lead 108a and 108b of the cathode part 106, an antenna lead 109, and an antenna ceramic 110 are provided.
In a magnetron disclosed in JP-P-2000-306518, a method in which the getter material 103 is filled between the cathode lead 108b and the metal sleeve 111 swaged to the cathode lead 108b in order to prevent axial movement of the ceramic 130 which supports the two cathode leads 108a, 108b forming the cathode part as shown in FIG. 10 and a method in which the getter material is applied to the surface of the cathode lead 108a between the cathode side end hat 112 and the ceramic 130 as shown in FIG. 11, are adopted. These two methods can be adopted at the same time (that is, the combination of filling the getter material into the metal sleeve 111 and applying the getter material to the surface of the cathode lead 108a). In addition, the getter material 103 may be applied to the surface of the anode side end hat 113.
When the getter material is applied to or sintered on the pole piece like the magnetron disclosed in U-S61-018610, however, the gettering effect is exerted sufficiently because of relatively low temperature of the pole piece. Typically, the temperature of the pole piece is about 200 degree Celsius at a maximum.
When the getter material is filled in or applied to the lead lines or the anode side end hat similarly to the magnetron disclosed in P-2000-306518, the temperature of the getter material is kept in high due to its position close to the filament. Typically, the filament temperature is about 1700 degree Celsius. In this case, although this high temperature is effective for activation of the getter material, the melting point of the getter material such as titanium and zirconium should be considered. As the melting point under 10−6 Pa condition according to the vapor pressure curve is about 1000 degree Celsius for titanium and 1300 degree Celsius for zirconium, the getter material filled in or applied to the lead line may evaporate due to thermal conduction from the filament. Once the getter material evaporates, the performance of the magnetron is dramatically deteriorated. Especially, when the getter material filled in or applied to the lead line and the end hat evaporates, the getter material is vapor-deposited to the stem ceramic and the antenna ceramic for insulation and therefore unwilling electrical conductions are possibly caused.
The present invention is achieved in view of above mentioned problems. The object of the invention is providing a magnetron which works in the temperature range suitable for efficient work of the getter material and which has stable electrical character and performance even when the getter material evaporates and the stem ceramic and the antenna ceramic are vapor-deposited.